Acid-catalyzed reactions such as alkylation, esterification, and isomerization are known in the chemical industry. Acid catalysts such as sulfuric acid, aluminum chloride, hydrogen fluoride, phosphoric acid, and paratoluenesulfonic acid have been used in these types of reactions in the past. However, a property of these acid catalysts is that they corrode metals, which has meant that the manufacturing equipment had to be made from expensive corrosion-resistant materials or subjected to an anti-corrosion treatment. Also, since in addition to the difficulty of separating the reaction substances after the reaction, a waste acid treatment was usually necessary, the process entailed complicated steps such as alkali washing, and caused a serious environmental problem. Furthermore, it was extremely difficult to recycle the catalyst.
In response to these problems, there has been proposed a sulfuric acid group-containing solid acid catalyst obtained by bringing a hydrated oxide or hydroxide of a metal from Group IV of the Periodic Table into contact with a sulfuric component-containing solution, then calcining at 350 to 800° C. (Japanese Patent Publication 59-6181). This solid acid catalyst exhibits a higher acid strength than 100% sulfuric acid (the Hammet acidity function H0 is −11.93). Because of its high acid strength, this solid acid catalyst provides good catalyst performance in a wide variety of acid-catalyzed reactions, and furthermore has low corrosivity, separation of reaction substances is easy, there is no need for waste acid treatment, and the catalyst can be recycled. As such, this catalyst is expected to supplant conventional acid catalysts in many kinds of industrial reactions.
It is already known that a catalyst comprising platinum added to a catalyst obtained by calcining a zirconia gel containing a sulfuric component exhibits good activity in hydrocarbon isomerization reactions (U.S. Pat. No. 3,032,599). As for methods for preparing a metal oxide catalyst containing a platinum group metal and a sulfuric component, which are intended primarily for the isomerization of hydrocarbons, a manufacturing method that omits the calcining between the treatment with a sulfuric component-containing compound and the step of supporting a platinum group metal, a manufacturing method in which the order of the treatment with a sulfuric component-containing compound and the supporting of a platinum group metal is reversed, and a manufacturing method in which the type of sulfuric component-containing compound is changed have been disclosed in Japanese Patent Publications 5-29503, 5-29504, 5-29505, and H5-29506. A method for preparing a platinum-containing zirconia sulfate shaping has been disclosed in Japanese Laid-Open Patent Application 9-38494.